The present invention relates generally to the recovery of phytic and lactic acids from mediums in which they are contained, and to the production of inositol. More particularly, it relates to methods for adsorptive recovery of phytic acid and/or lactic acid, and also to methods for treating phytic acid or derivatives thereof to obtain inositol.
Phytic acid (inositolhexaphosphoric acid) occurs naturally in plant tissues, and, of particular commercial interest, in the seeds of many cereal grains. Generally, this phytic acid occurs as its insoluble calcium-magnesium salt, also known as "phytin". At present, commercially available phytic acid is derived largely from corn steep liquor and/or rice bran, which typically contains phytin at levels corresponding to about 2 weight % phytic acid.
In the past, phytin has been recovered from such mediums by precipitation. For example, the medium may be treated with an organic or inorganic acid to extract phytin, which can then be precipitated. Calcium compounds such as calcium hydroxide can also be used to precipitate the desired material as calcium phytate. However, in these precipitation methods, considerable cost is involved in the recovery and purification of the phytin material. Further, many undesirable waste products are often produced, and significant amounts of the target material are lost during processing.
In another facet of study in this area, adsorption/desorption processes have been proposed for recovering phytin. For example, in earlier work, W. Ledding et al. suggested a process in which steep water is passed over an ion retardation resin. See, U.S. Pat. No. 3,410,929 (1968). According to this patent, the resin contains a mixture of anionic and cationic groups. As an illustration of the type of resins to be used, the patent describes an adsorption process using Dow Chemical Company Retardation 11 A8 resin. This resin was made by polymerizing acrylic acid within the pores of a strong base resin, Dowex Resin 1. After adsorption of the phytin, the loaded resin is rinsed with water and the phytin desorbed using a salt (NaCl) solution.
Following this earlier work by Ledding et al., Ogawa et al., in U.S. Pat. No. 4,668,813, described obtaining phytin by treating a phytin-containing solution with an ion-exchange resin. As stated in the patent, the phytin-containing solution is passed through a bed of an anion-exchange resin (e.g. strong ionic base OH.sup..crclbar., CH.sub.3 COO.sup..crclbar., or Cl.sup..crclbar. -type resins exemplified in the patent). After water wash of the phytin-loaded resin, aqueous sodium hydroxide is passed through the resin bed to thereby elute the phytin as its sodium salt, which can then be converted to phytic acid.
Phytic acid per se has many uses, for instance as a metal chelator in animal fat and vegetable oil processing, as a rust inhibitor, in the treatment of hard water, as a nutrient, etc. However, phytic acid also enjoys substantial utility as an intermediate to its corresponding alcohol. In turn, this alcohol, commonly known and referred to as inositol, has wide application in medicine, nutrition, and also as an intermediate to still other useful compounds. As to its preparation, inositol has been obtained from phytic acid by hydrolysis with water at 100.degree. C. See, D. J. Cosgrove, "Inositol Phosphates", Elsevier, Amsterdam, 1980, p. 36. Inositol has also been obtained by hydrolysis of phytin with steam under pressure in an autoclave, See, F. A. Hoglan et al., J. Am. Chem. Soc., 1940, 62, 2397, and U.S. Pat. No. 2,112,553, as well as by hydrolysis of sodium phytate with water at elevated temperature and pressure in an autoclave. H. Ogawa et al., U.S. Pat. No. 4,668,813.
Other valuable materials also occur in mediums containing phytic acid. For instance, lactic acid occurs along with phytic acid in corn steep liquor. Lactic acid has also long been used in the food industry, in the production of confectionary products, soft drinks, beers, wines, dairy products, baby foods, jams, salad dressings, etc. Lactic acid is also used in the preparation of pharmaceuticals, cosmetics, agrichemicals, etc. Recently, there has been substantial academic and commercial interest in lactic acid as a potential raw material for producing biodegradable plastics. See, for instance, Lipinsky, E. S., and Sinclair, R. G., Chem. Eng. Prog., Aug., 26, (1986).
Commercially, lactic acid is at present produced via both synthetic and fermentation processes. The synthetic process converts lactonitrile to lactic acid, with the lactonitrile starting material being available as a byproduct in acrylonitrile production. Van Ness, J. H., "Hydroxy Carboxylic Acids," in Encyclopedia of Chemical Technology, 3rd Ed., Wiley, Volume 13, pp. 80-103 (1981). On the other hand, in traditional fermentation processes, lactic acid bacteria produce free lactic acid as they metabolize carbohydrate raw materials. As it is formed, the lactic acid is typically neutralized by an alkali such as NaOH, NH.sub.4 OH or more commonly CaCO.sub.3 to prevent a pH drop in the fermentation broth. Following the fermentation, the broth is acidified to convert the lactate salt to free lactic acid which is then separated from the broth. See, Buchta, K., "Lactic Acid", Biotechnology, H. Dellweg. Ed.), 3, 409 (1985). However, as has been recognized, this separation and purification is particularly cumbersome and inefficient. Atkinson, B. and Mavituna, F., Biochemical Engineering and Biotechnology Handbook, the Nature Press, N.Y. (1983). Thus, the search for new commercially attractive lactic acid sources and recoveries has continued for some time.
It is in light of this extensive background that the applicants applied themselves in an effort to address the continuing need and demand for truly convenient and effective recoveries of phytic and lactic acids, and conversions of phytic acid or derivatives thereof to inositol. Through their discoveries, the applicants have now succeeded in addressing these needs.